This section provides background information related to the present disclosure and is not necessarily prior art.
Vehicles such as automobiles are commonly equipped with seat adjusters that raise and lower the driver and passenger seats. Such seat adjusters may be manually operated or power operated. Manually operated seat adjusters commonly employ a knob that is manually rotated by a vehicle occupant to raise and lower the seat. Other versions of manually operated seat adjusters employ a lever that is pushed or pulled by the vehicle occupant to raise and lower the seat. Power operated seat adjusters are typically driven by an electric motor that is actuated by one or more occupant controlled switches. Regardless of whether the seat adjuster is manually operated or power operated, the seat is typically raised and lowered by rotation of a pinion member or shaft that is meshingly engaged with a sector gear. The sector gear has a wedge-like shape and can be thought of as a slice or portion of a larger circular gear. For example and without limitation, the sector gear may have a limited radial extent of 45 degrees or less. The sector gear is pivotally supported on the vehicle and is pivotally coupled to a frame of the seat adjuster. Rotation of the pinion member in one rotational direction causes the sector gear to pivot in a downward direction, which drives the frame of the seat adjuster up. Rotation of the pinion member in an opposite rotational direction causes the sector gear to pivot in an upward direction, which lowers the frame of the seat adjuster. The seat of the vehicle is attached to and supported on the frame of the seat adjuster such that the seat is moves up and down with the frame of the seat adjuster.
When the vehicle occupant is seated, there is a large amount of force placed on the frame of the seat adjuster and thus the sector gear. Accordingly, a gear assembly with a high gear reduction is typically used to drive rotation of the pinion member. Such gear assemblies typically include several metal gears that are disposed in meshing engagement with one another. One drawback to existing gear assemblies is that the metal gears make noise when the seat is raised and lowered. Gear related noise is a nuisance to vehicle occupants and is perceived as originating from a faulty or poor quality component. This problem results in numerous service and repair requests.
Some of the most important requirements for automotive seat adjusters include: the range of reduction ratio, the range of output torque, size, weight, efficiency, the level of noise produced by the automotive seat adjuster, shock load capability, cost, durability, and the amount of backlash. For some applications, such as those used in adjusting and maintaining the adjusted position of a vehicle seat, a special requirement called anti-back drive capability is also required. Anti-back drive capability may also be referred to as “non-back drive capability,” “self-locking capability,” or “anti-regression capability.” Gear drives transfer the high speed and low torque rotation of an electric motor input shaft to low speed and high torque rotation of an output shaft, in either, a clockwise (CW) or a counter-clockwise (CCW) direction of rotation. For gear drives with anti-back drive capability, any attempt to transfer torque from the output shaft back to the input shaft by applying an external load (e.g. occupant weight or external reaction forces in the case of a crash accident, etc.) to the output shaft is prevented. This protects against damage to the electric motor and ensures that the vehicle seat maintains its position when the electric motor is not energized. Back drive can also occur, at a much slower rate, as gravity, coupled with road vibration, tends to slowly back drive the seat mechanism downward over time.